Base oil is the major constituent in finished lubricants and contributes significantly to the properties of the engine oil. Engine oils, for example, are finished crankcase lubricants intended for use in automobile engines and diesel engines and contain two general components, namely, a base stock or base oil (one base stock or a blend of base stocks) and additives. In general, a few lubricating base oils are used to manufacture a variety of engine oils by varying the mixtures of individual lubricating base oils and individual additives.
According to the American Petroleum Institute (API) classifications, base stocks are categorized in five groups based on their saturated hydrocarbon content, sulfur level, and viscosity index (Table 1). Lube base stocks are typically produced in large scale from non-renewable petroleum sources. Group I, II, and III base stocks are all derived from crude oil via extensive processing, such as solvent extraction, solvent or catalytic dewaxing, and hydroisomerization. Group III base stocks can also be produced from synthetic hydrocarbon liquids obtained from natural gas, coal or other fossil resources, Group IV base stocks are polyalphaolefins (PAOs), and are produced by oligomerization of alpha olefins, such as 1-decene. Group V base stocks include all base stocks that do not belong to Groups I-IV, such as naphthenics, polyalkylene glycols (PAG), and esters
TABLE 1API classificationGroup IGroup IIGroup IIIGroup IVGroup V% Saturates<90≥90≥90Polyalpha-All others% S>0.03≤0.03≤0.03olefinsnotViscosity80-12080-120≥120(PAOs)belonging toIndex (VI)group I-IV
Base oils are generally produced from the higher boiling fractions recovered from a vacuum distillation operation. They may be prepared from either petroleum-derived or from syncrude-derived feed stocks or from synthesis of lower molecular weight molecules. Additives are chemicals which are added to base oil to improve certain properties in the finished lubricant so that it meets the minimum performance standards for the grade of the finished lubricant. For example, additives added to the engine oils may be used to improve oxidation stability of the lubricant, increase its viscosity, raise the viscosity index, and control deposits. Additives are expensive and may cause miscibility problems the finished lubricant. For these reasons, it is generally desirable to optimize the additive content of the engine oils to the minimum amount necessary to meet the appropriate requirements.
Formulations are undergoing changes driven by a need for increased quality. For example governing organizations (e.g., the American Petroleum Institute) help to define the specifications for engine oils. Increasingly, the specifications for engine oils are calling for products with excellent low temperature properties and high oxidation stability. Currently, only a small fraction of the base oils blended into engine oils are able to meet the most stringent of the demanding engine oil specifications. Currently, formulators are using a range of base stocks including Group I, II, III, IV, and V base stocks to formulate their products.
Industrial oils are also being pressed for improved quality in oxidation stability, cleanliness, interfacial properties and deposit control.
Despite advances in lubricating base oils and lubricant oil formulation technology, there exists a need for improving oxidation performance (for example, for engine oils and industrial oils that have a longer life) and low temperature performance of formulated oils. In particular, there exists a need for improving oxidation performance and low temperature performance of formulated oils without the addition of more additives to the lubricant oil formulation.